Planographic printing plate comprising a polyacid organic intermediate layer



June 9, 1964 F. DOWDALL ET AL RLANoGRAPx-I'Ic PRINTING PLATE coMPRIsING A PoLYAcID ORGANIC INTERMEDIATE LAYER Filed July 25, 1955 /ZH A mrfzl my /ffW/f// F/ci. 4

United States Patent O ELANGGRAPHEC PRENTKNG PLATE CMPRISHNG A PLYACHD i) R G A N ll (I NTERMEDEATE LAYER .lohn F. llowdall, St. Paul, and .lohn M. Case, Mounds View Township, Ramsey County, Minn., assignors to Minnesota Mining @e Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed July 25, 1955, Ser. No. 523,951 8 Claims. (Cl. 9er- 75) This invention relates to planographic printing plates. It particularly concerns plates of a type which may be usedl on well-known commercial forms of lithographie presses.

ln quite recent years, for the iirst time to our knowledge, a dimensionally stable presensitized lithographie plate has been made, in the manner described and illustrated in the eopending application of Clifford L. Jewett and John M. Case, Serial No. 519,900, to be issued on July 26, 1955, as Patent No. 2,714,066. Said application Serial No. 519,900 is a division of the earlier Jewett and Case application Serial No. 450,149, filed August 16, 1954, and the latter, in turn, is a continuation-in-part of the Jewett and Case application Serial No. 199,566, filed December 6, 1950, now abandoned. The present invention is in the nature of a further development of said invention of Jewett and Case, and is particularly concerned with presensitized planographic printing plates in which the light-sensitive diazo resin or other equivalent light-sensitive organic material is bonded to the surface of a dimensionally stable metal plate, and protected from any degradation such as might normally be induced by the metal surface, by means of a thin intervening ilm of a reaction product of the metal surface and a watersoluble film-forming organic polyacid polymer; in this respect see the disclosure at column 9, lines 47-54 of said Jewett and Case Patent No. 2,714,666. This invention thus provides a specific novel dimensionally stable presensitized lithographie plate having an acid surface-treatment in lieu of the inorganic treatmentV described and illustrated in the aforesaid Jewett and Case applications and patent, and adapted for use in lieu of the treated product thereof.

insofar as `we are aware, no one has ever produced any commercially acceptable presensitized metal-backed planographic plate prior to the invention disclosed and claimed in the aforesaid Jewett and Case application and U.S. Patent No. 2,714,066; and no one likewise has ever previously produced any presensitized planographie plate which will compete with grained zinc platesof the prior art where a long press life and quality reproductions are important. No one, prior to the present invention, ever visualized that aluminum or other metal plates could be used to receive a coating of a light-sensitive diazo resin, or the like, by the simple expedient of irst briefly treating the metal surface with a dilute aqueous solution of' an organic polymeric film-forming polyacid, which then pro'- vides a surface which effectively inhibits degradation of the diazo resin coating, and to which the exposed insolubilized diazo resin will lastingly adhere.V The acidic polymer treatment does not measurably increase the thickness of the metal plate. The surface of the treated plate is itself hydrophilic or is readily rendered hydrophilic by conventional treatment. This ability of organic polyacid materials to react with or adhere to the metal surface suficiently to provide the image-retaining andl stabilizing surface as above described would not be expected.

Therefore, one of the purposes of this invention is to provide organic polyacid treated planographic plates which are presensitized, i.e., are-ready for an exposure through a negative or stencil without further treatment, yet which 3,136,636 Patented .lune 9, 1964 can be stored for considerable periods of time and still be used. A further object of our invention is to'provide a presensitized plate which preferably is free of surface roughness of grain, and from which sharp-lined impressions can be produced and from which printing of high resolution, that is, extreme clarity of detail of the printed' matter, can be obtained. A further object is to provide a presensitized lithographie plate of high dimensional stability which will be suitable for applications Where accurate registration is required such, for example, as in multicolor work, where the same sheet is successively printed from different lithographie plates. Another object is to provide a commercially acceptable presensitized lithographie plate. Other objects and advantages will appear from the description taken as a whole.

To illustrate a preferred form of our invention, reference is made to the appended drawing, in which:

FGURE 1 shows an aluminum sheet 10, in brokenaway view, having a thin protective image-retaining film l1, obtained by treatment with a water-soluble organic polymeric film-forming polyacid, tightly and chemically bonded to one surface yof the aluminum sheet 10;

FGURE 2 is like FIGURE 1 but additionally has a thin coating-1 2 of a water-soluble light-sensitive diazo resin coated over or absorbed by the said organic hydrophilic polyacid polymer coating;

FlGURE 3 is like FIGURE 2 except the plate of FIG- URE 2 has been exposed to ultraviolet light through a photographic negative and then washed with water or standard gum arabic solution, leaving the hydrophobic and organophilic diazo image 12a.

FIGURE 4 is like FIGURE 3 except that the exposed plate of FIGURE 3 has its image surface wiped with an image developer, leaving an extremely thin coating of image developer 13. v

All dimensions in the drawing are greatly exaggerated for clarity of illustration The aluminum sheet 1li, though being a foil having a thickness of only about .005 to .012 inch, is shown in broken-away view, in respect to its thickness as well as its length, toy illustrate the fact that the organic polymeric film-forming polyacid treatment 11 is really very thin compared with the aluminum foil lll. The said treatment is probably little more than a monomoleeular layer.

The coating of diazo light-sensitive resin 12 is shown in the drawing as also being a very thin coating, but it is not the intention in the drawing to illustrate whether the light-sensitive diazo resin coating is equal to, greater than, or less than the thickness of the organic polyacid treatment. sorbed to some extent in the treated surface.

A salient embodiment of our invention consists in providing an extremely thin treatment or lm, probably often substantially of monornolecular thickness, of a watersoluble organic polymeric film-forming polyacid on a surface of a given metal plate, for example, an aluminum plate. The aluminum plate may be from .005 to .012 inch in thickness, although this obviously depends upon the'type of press on which the plate is to be employed and other factors, and these dimensions may be greatly varied as circumstances permit. Over the exposed 0rganic polyacid treated surface, we apply a thin coating of preferably a water-soluble light-sensitive diazo resin. This product, following drying, may be packaged in any convenient light-proof container, and shipped to the customer in a distant city or state. When the customer desires to use the plate, which may be many weeks, or even months, after the plate was manufactured and shipped to him, he will remove the plate from its package under subdued light, place it in contact with a negative or stencil, then expose it to a source of ultraviolet light for a short period of time, eg., from 1 to 5 minutes, de-

Actually, the diazo coating is apparently ab-y 3 pending upon the'intensity of the ultraviolet light, and then wash the surface of the plate with water, whereupon the unexposed diazo material (that shielded by the stencil or negative), which remains water-soluble, is cleanly washed off, leaving the polyacid treated surface exposed in those areas. The portion of the diazo coating which was exposed to the ultraviolet light was thereby insolubilized and rendered hydrophobic and organophihlic (that is, water-repellent and ink-receptive), expelling nitrogen from the molecule in the process.k During such exposure and insolubilization of the diazo light-sensitive material it becomes very strongly bonded to the surface of the said organic film. This plate is then ready to be placed on a lithographicrpress, and used in printing or reproducing the desired writings or images. However, before placing it on the lithographie press, it is advantageous to treat the printing surface of the plate with what, for want of a better term, might be referred to as an image developer. The image developer may take various forms. One example is a pigmented resin emulsion which will adhere to the ink-receptive areas but will not adhere to the hydrophilic areas of the plate. A printers developing ink can also be used as an image developer. An example of an image developer, which we have found to be particularly useful, is described in a copending application of Myron W. Hall, entitled Planographic Printing-Plate Image Developer, Serial No. 239,841, filed August l, 1951.

The image developer is of this practical importance: Prior to the application of the image developer, the image is not visible. lf a plate in that form is presented to the lithographer or printer, he cannot be sure whether he is putting the plate on the press correctly or whether he has it backwards. Additionally, in the absence of the visible image, the pressman would not knowwhether he had an exposed plate, unless this were denoted by some coding system or such like. In addition to making the image visible, so the pressman can see it, a good image developer also (a) helps the plate to ink up more readily when placed on the press, and (b) strengthens the image so that more copies can be ,run from a single plate, while still getting clear reproductions.

Having now described generally our novel planographic plate, the same will be more specifically described with the aid of several specific but non-limitative examples.

Example l Aluminum foil or sheet material of about .005 inch in thickness is first made ready for treatment. Since greasy lubricants are commonly used in aluminum mills during the rolling operation, it is first desirable to treat the aluminum foil or sheet so as to remove any greasy film, so that the surface exposed will be an aluminum surface. One method which we have found to be advantageous in cleaning the aluminum surface is to immerse the same in a 20% solution of tri-sodium phosphate for a sufficient time only to clean the aluminum, e.g., for a period of 5 minutes. The temperature of the solution may be controlled at approximately 160 F. Higher temperatures may be used with a corresponding reduction in the time of treatment, and lower temperatures may be used with a corresponding increase in the time of treatment; and other solution concentrations may be used, if desired. The cleaning or de-greasing of the aluminum foil or sheet material in the manner outlined above will often develop a black scum or residue on the surface of the aluminum (which probably consists primarily of oxides and hydroxides of alloyed metals) which must be either thoroughly wiped or washed away mechanically or dissolved in an acid solution such, for example, as concentrated nitric acid. lf there is no scum, then there is nothing to clean away; but if there is a black scum, we have found that nitric acid of about 70% concentration, employed at room temperatures, will clean the scum off of the surfaces of the aluminum foil or sheet material and leave it in good condition for the subsequent steps of oui` plate-making operation. (Aluminum is passive to 70% nitric acid.) After treatment with the acid solution, the aluminum foil or sheet material is thoroughly rinsed with water to remove any residual acid.

The cleaned surface'of the aluminum is then treated,

temperature) with the immersion time for any portion of the sheet being about S seconds. During this time the organic polyacid in contact with the surface of the sheet reacts therewith. The sheet is then led through a bank of water washing sprays where any excess unreacted polyacrylic acid is removed. After being washed, the sheet is then dried at room temperature.

The resulting polymeric organic polyacid treatment exists on the sheet as a very thin hydrophilic film. It appears to be chemically bonded to the aluminum and can only be abraded away by penetrating the surface of the aluminum. The treated aluminum sheet will not oxidize to a hydrophobic surface upon exposure to air as an untreated sheet will quickly do. Thus is provided a permanently hydrophilic scum-preventing and tone-reducing iilm or treatment which will tenaciously retain an insolubilized diazo resin image thereover as will be hereafter shown.

The polyacrylic acid treated aluminum foil or sheet just described is of quite a smooth character and usually f has a metallic sheen or relatively smooth appearance, as

contrasted with the dull appearance of various prior art grained plates. While some very slight amount of etching may unavoidably occur on the aluminum surface of the sheet during the cleaning operation, this is so slight that it does not impart to the finished treated sheet a rough surface of a matte appearance. This isV important in securing the highest performance characteristics, sought after in our finished presensitized lithographie plates, particularly where line line Work or fine half-tones are being reproduced.

We have found it advantageous to apply our polymeric organic polyacid treatment to the plate surfaces in rather dilute solutions, that is solutions containing in the order of 1-5 percent solids or less, in order to facilitate the removal of unreacted material by washing. Where thicker more viscous solutions are applied the quantity of unreacted material is greater requiring a more extensive and careful washing of the plate. However, if desired this may be done without any deleterious effect to the plate.

If desired, the metal plate surfaces may be swabbed with a cloth or equivalent material previously wet with the solution rather than dip coated. We nd this technique of application to be preferable where the solution is of a syrupy or viscous consistency to avoid deposition of an overly' thick film, the unreacted excess of which would be diflicult to wash away from the surface.

Our treated sheet is next treated with a solution of Va light-sensitive diazo resin or equivalent. One suitable method of making a suitable light-sensitive diazo resin is as follows: Thirty-four parts of the sulfate salt of paradiazodiphenyl amine (available, for example, from the Fairmount Chemical Company, Newark, NJ., at the present time as Para-Diazodiphenyl Amine Salt) is mixed with 3.25 parts of paraformaldehyde and 4-5 parts of anhydrous zinc chloride. The above mixture is gradually introduced into 135 parts of cool sulfuric acid of 66 Baum, care being taken that the temperaturedoes not exceed 6 C. When poured on twice its weight of ice, the brown solution (obtained from the U zinc chloride solution tothis aqueous diazo resin solution precipitates a yellow solid which is removed; this yellow solid is then further purified by dissolving in water and precipitating by the addition of alcohol. This new precipitate is the purified light-sensitive diazo resin and, in the form of a dilute solution in water, for example, about a 1% solution, is used in applying a light-sensitive coating to our aluminum sheet or the like, above described, which has been given the polyacrylic acid treatment and thus provided with a scum-preventing and tone-reducing ilm overlying and in contact with the surface of the metal, as herein illustrated.

The reactions and precipitations employed in the making of the light-sensitive diazo resin are carried out under subdued light, for example, under a yellow light. This is also true of the operation of coating the hydrophilic surface of the aluminum sheet with a dilute solution of the light-sensitive diazo resin or equivalent.

The dilute solution of light-sensitive diazo resin, just described, may be applied to the exposed surface of the polyacrylic acid polymer treated panel, above described, by a roll coating method, for example. Running the sheet in pressure contact with a rotating rubber roller, which is wet with the dilute diazo solution, applies, a thin continuous coating of the d iaZo solution over the surface. It is preferred that the diazo coating be an extremely thin one, for example, leaving a residue of about 0.003 gram, or even less, e.g., 0.001 gram, of the diazo resin per square foot of plate area. For special purposes, e.g., to obtain a visible image after exposure, a heavier residue of diazo resin, but still a thin film, can be coated on the surface. When the diazo coating is dried, the treated and sensitized sheet is then die cut to standard plate sizes and, continuing under subdued light, the plates are packaged in light-tight packages, in which they are sent to the users and customers. The customer,

in using the same, removes them from the package under subdued light and places a negative or stencil thereover and exposes the saine to ultraviolet light, to produce the desired image, as already described hereinabove.

Sensitized plates made according to ourV above de scribed method are more sensitive to light than conventional albumin,` ammonium bichromate plates; and our plates can be sufficiently exposed in about two-thirds the time required for such prior art plates.

Scratches, iingerprints and other foreign matter will impair the light-sensitive surface, and the plate, therefore, shouldbe handled carefully, by the edges. After the plate has been exposed, if it is going to be stored for a period of time, a desirable precaution is to coat the plate with a gum arabic solution, which gives mechanical protection to the image and then can easily be washed oli with water when it is desired again to use the plate.

Exposure of our presensitized lithographie plates may be carried out in a printing frame under a source of ultra-violet light. Carbon arcs may be used but are not required. Photo-lood bulbs and black ligh fluorescent tubes will also give satisfactory results. While the exposure time is not critical, under-exposure may result in broken images or no image at all. Extreme over-exposure may cause dirty highlights and blocked-up Vshadows in half-tone areas. While the user of our presensitized plates has considerable latitude in the amount of exposure, the fore-going will serve to guide him from undue extremes of overexposure or under-exposure.

Suggested exposure times for the following light sources are:

Min. Bank of l5 watt BL light tubes at 6 2-4 35 amp. carbon arc at 24" l-2 After exposure 'the plate (where adiazo resin is used as the sensitizer) is desensitized by wiping with a solution of gum arabic, which dissolves and removes the unreacted diazosensitizer. At this point the image is invisible.

While the plate is still wet with the gum arabic solution, an image developer or a strengthener consisting of a resin emulsion (or, alternatively, ak printers developing ink of conventional type) is poured on the plate and rubbed in quickly with a soft pad or cotton wad. The excess image developer should be wiped away before it driescompletely. The resinous portion of the image developer should preferably contain a pigment or dye which will make the image clearly visible as the particles of resin adhere to the hydrophobic and organophilic image. The plate is then ready for the press, or it may be coated with gum arabic if it is to be stored before use.

Our lithographie plates require the use of less water on a lithographie press than is required where the conventional prior art grained Zinc plates are used. This is a factor in giving more brilliant colors in lithographie reproductions made from our plates, since the reduction of color brilliancy caused by ernulsilication of water and ink in the case of grained. zinc plates is greatlyI minimized where our plates are used. n

`iii/here our plates are used, less ink is also required to give the same tone values in the linished work, and especially so in multicolored printing, 'thereby significantly reducing the drying time required between the printing of successive colors.

After our plate (made, for example, with a diazo lightsensitive resin) has been installed on a lithographie press,

the gum arabic coating (if previously applied) is removed by sponging with water or with a weak fountain solution. The fountain rollers should be dropped lirst and, after a few revolutions, the ink rollers may be dropped. The image should ink up quickly. No special. inks or fountain solutions are required, and most materials cornmonly used for this purpose will be found to be satisfactory for use with our plates. ln order to obtain the maximum number of satisfactory impressions, the press should be carefully adjusted to the least pressure consistent with quality printing.

Our lithographie plates are of such nature, due to the particular materials and the thickness thereof, that they do not wrinkle or stretch during processing or on the press (as do paper or plastic planographic plates, for example) and, therefore, are particularly suitable for lithographie printing, even where very accurate registration is required.

We have found that nlm-forming water-soluble homologues of polyacrylic acid may be employed in the treatment of our novel lithographie plates. yFor example, an excellent permanent hydrophilic scum-preventing surface has been found to be provided on the surface of the metal sheet when a solution of an allryl homologue, polyrnethacrylic acid, is used. Good adhesion of the reaction lightsensitive resin is obtained tosuch a surface. Thus the resulting plate exhibits a lengthy press life.

Example Il The aluminum plate, a surface of which has been cleaned in the manner described in Example I, is continuously dip-coated in an immersion bath containing a one percent solution of the sodium salt of carboxymethyl cellulose, such as that presently obtainable from the Hercules Powder Company as CMC containing an average of about 0.7 substituted carboxymethyl groups per anhydro glucose unit (theoretical maximum of 3). Temperature oi the bath is maintained at about 25-30" C. although higher temperatures may also be used. The diptime or period in which any portion of the aluminum sheet remains in the bath is about 5 seconds although no harm is done if the period exceeds this period. After ybeing coated with the solution, the sheet is washed with water to remove excess unreacted polymer and then dried for about l0 minutes in an oven heated to about 25.0 F.

The resulting treated sheet contains a permanently hydrophilic surface which will not oxidize to a hydrophobic surface even upon standing exposed to air for many months. After being presensitized by coating with a lightample the sheet may be stored for weeks or months without deleterious effect. Upon subsequent exposure through a negative, a highly suitable commercially attractive lithographic plate is obtained which, when properly installed and operated on a standard lithographie press, will yield several thousands of excellent reproductions.

While the organic polyacid employed in the present example is in the form of the soluble sodium salt, the products obtained with this and other soluble salts of the polycarboxylic acid polymers and strongly alkaline materials are fully equivalent to, if not identical with, the products obtained with the free acids; and hence these salts are to be considered the full equivalents, for the purposes of this invention, of the free acid polymers.

It is to be noted that the temperature at which the washed organic polyacid treated plates are dried is not critical, any temperature which will not decompose the treatment or otherwise adversely affect the sheet being suitable. In fact, We have in some instances prepared suitable lithographie plates where 'the light-sensitive coating was applied after the treated sheet was washed but before it was completely dried.

Example III A permanently hydroptnlic scum-preventing and imageretaining surface treatment is applied to a surface of 0.005 inch thick aluminum foil or sheet which has been cleaned in the manner described in Example l. The surface is applied by dip-coating the sheet in a dilute solution (about one percent) of carboxymethylhydroxyethyl cellulose for about l seconds followed by a thorough water Wash and subsequent drying for about l0 minutes at 250 F. A suitable carboxymethylhydroxyethyl cellulose contains an average carboxymethyl substitution of 0.45 group per anhydro glucose unit and a hydroxyethyl substitution of 0.25 group per anhydro glucose unit. A water-soluble polyacid cellulose ether derivative similar to the one here employed is marketed by the Hercules Powder Company under the trade name of CMHEC and prepared according to British Patent No. 670,672.

As in the case of the lithographie plate of Example Il, in which a surface treatment of carboxymethyl cellulose is employed, a plate is obtained which, when coated with a light-sensitive diazo resin as previously described, will not decompose or become degraded upon storage, under subdued light or in a light-proof container, even for several months. After exposure of the plate and the use of the image developer in the manner described in Example I, we have been able to obtain many thousands (over 25,000) of clear and arcuate reproductions from a single lithographic plate of the present example.

Example IV A highly satisfactory experimental presensitized lithographic plate is obtained in the following manner: A magnesium foil or sheet of about .005 inch in thickness is cleaned by solvent degreasing with trichloroethylene and treated with a dilute aqueous one percent solution of the film-forming linear vinyl addition product of stoichiometric quantities of methyl vinyl ether and maleic anhydride. A copolymer of this type may be obtained in powder form from General Aniline & Film Corp. under the trade name of PVM/MA. The solid is easily dissolved in hot water to form a treating solution. The sheet is then treated by swabbing the surface with a cloth wet with the solution, rather than by dip-coating. The temperature of the solution is maintained at about normal room temperature although higher temperatures may be used. Contact time of the coated solution with the cleaned aluminum surface may be as little as 2 seconds although 5-10 seconds is preferred. Excess, unreacted material is then washed of the surface and the sheet dried.

A permanently hydrophilic scum-preventing surface results, which appears to be chemically bonded to the aluminum surface. A presensitized lithographie plate is obtained by application of a light-sensitive diazo resin coating over the treated surface which remains stable when stored in light-proof containers for several months. When exposed through a negative the reacted diazo compound is adherently attached to the surface permitting high quality reproductions to be obtained.

In the present examples the organic polyacids employed are Water-soluble. We have found an aqueous medium to be necessary to the proper reaction between the polyacid and the metal surface. Where the metal plate is cleaned with an aqueous solution, the polyacid treatment may be applied immediately to the freshly cleaned and` washed surfaces. No intervening drying period in which the plates could become dusty or soiled, thus spoiling the surface, is necessary.

yThe organic polyacid compounds applied to the metal surface in each of the specific examples is a polyacid, that is contains many acid groups in each molecular chain. Polymers which contain no acid groups do not provide a surface to which the light-sensitive diazo resin, or equivalent, will adhere upon exposure. Polymers which contain very few acid groups in the chain, such as condensed linear polyesters, ineffectively react with the aluminum plate. However, these latter mentioned polymers, insofar as we are aware, are not Water-soluble and are thus additionally unsuitable. In the case of carboxymethyl cellulose and carboxyrnethylhydroxyethyl cellulose, the watersoluble derivatives, i.e., those containing sucient ether groups to render the polymer soluble, provide polyacids which properly bond the reacted diazo image to the plate.

All of those organic polyacid polymers employed in the examples are seen to be hlm-forming, i.e., a solution of the polymer may be cast into a self-sustainin g continuous film, as for example, by spreading a thin film of a water solution of the polymer with the aid of a small knife-coating apparatus onto a releaseable liner carrier web, drying the lm and separating it from the web. We have found that the use of a film-forming polyacid polymer is necessary to attain firm anchorage ofthe exposed insolubilized image to the surface of the sheet and to provide the essential inhibition to degradation of the light-sensitive resin. Where low molecular weight nonlni-forrning polymers are employed, the insolubilized image may be rubbed from the sheet with the hands. Further, the diazo resin decomposes rather rapidly, presumably by reaction with the metal plate.

Other Water-soluble polymeric film-forming organic polyacids thanrthose above specifically mentioned are suitable in the preparation of the lithographie plates hereof. For example, treatment of the plate with a solution of sulfomethyl cellulose, formed by inter-reaction of chloromethanesulfonic acid and alkali cellulose, provides a permanently hydrophilic protective image-retaining surface on the plate. Other water-soluble polymeric film-forming organic polyacid compounds, notably, lignosulfonic acid or the lzl copolymer of styrene and maleic anhydride are equally effective in providing excellent protective imageretaining surfaces. While these particular treatments do not directly provide the hydrophilic plate surface, as do the other examples which contain greater numbers of hydrophilic groups in the molecular chain, by the simple expedient of wiping the plate, after exposure, with a gum arabic solution and rubbing to dryness (as is the usual practice in the lithographie art), the non-exposed surfaces of the plate become selectively hydrophilic; thus are provided high quality lithographie plates.

One advantageous type of aluminum foil to be used for our process, in the manner above described, is one produced by the Aluminum Company of America and designated :as 3003Hl9, the same containing about 1.25% manganese alloyed with the aluminum. There are some other types of aluminum foil or sheeting which would be too soft and pliable to be Well suited for our use if employed in the form of relatively thin gauge sheets, al-

arse-,ese

though any commercial type of aluminum which is stiff enough to resist wrinkling and creasing, in the form of thin sheets or foil, may be employed.

While aluminum appears, at present time, to be our preferred metal backing sheet material, onl the basis of cost, handling properties and such like, we have alsosuccessfully employed sheets of lithographie zinc, foils of copper, lead and tin, electro-deposited chromium and copper surfaces, sheets of commercially pure magnesium, polished sheets of tantalum and a sheet of titanium known as Ti-75A, treating the same asa'oove illustrated, to render the metal surface capable of being hydrophilic and scum-preventing and to provide a-lilm or surface to which an insoluble diazo image will strongly adhere. Still other metals may be employed in making our presensitized planographic plates, so long asa strongly adherent or chemically bonded water-soluble organic polymeric filmforming polyacid treatment can be applied thereto, with suitable control of conditions, buty we believe the amphoteric metals, as a class, provide the best surfaces on which to apply our protective image-retaining surface treatments. f

Diazo materials, especially diazoI resins, have been described herein as the preferred light-sensitive materials for our purposes. However, variations in this regard are contemplated.

It has been found, for instance that the azide of our preferred diazo resin can, with suitable modifications, be used as the light-sensitive coating. This polymeric azido resin is not water soluble and only slightly soluble in common organic solvents, but a concentration suitable for coating can be obtained using as solvents toluene or methyl Cellosolve, or mixtures of these, or other organic solvents. After exposure'through'a negative or stencil the un-light-decomposed azide canrconveniently be removed by a Water-toluene mixture, leaving a hydrophobicl printing image of water-insoluble, light-reacted azide.`

It is possible to prepare and use, as light-sensi terials, other polymeric azido resins, particularly aromatic azido resins, which seem to be particularly useful, and also aliphatic azido resins. Similarly,` diazo oxides (see The Aromatic DiazoComuounds, by H. K. Saunders, published 1949 by Edward Arnold aY Co., London, page 29 thereof), both mono and poly-molecular have been found to be useful light-sensitive compounds in making our plate. The mono-molecular imino-quinone-diazide (see page 24 of said book by Saunders) made from the monomer of our preferred diazo resin has also been found to be useful. Certainvpara-tertiary-amino-diazo resins can be prepared and are useful. The preparation offpolyvinyl cinnamate light-sensitive materials has been recently disclosed and at least certain of these materials have been found to be useful` in the practice of this-invention.

The light-sensitive diazo resin, or equivalent, need not be immediately applied to our organic polyacid treated metal surface. On the contrary the light-sensitive material may be applied at substantially any time after the treatment is applied." Thus' the4 surface treatment maybe applied in one place, or locale and, if desired, the treated plate may be shipped to a distant point and the lightsensitive diazo coating applied at some future date. When so handled, our treated sheets need not be shipped in light-proof containers. Care must be taken, however, as in the-instance of the presensitized sheet, to protect and preserve the treated surface from abrasion, contamination, etc.

Where the light-sensitive material is to be applied to the treated surface a substantialperiod of. time after application of the image-retaining surface, it Vis generally desirable to Wash the treated surface prior to application of the light-sensitive material. The washing step may normally be effectively accomplished by merely swabbing the surface of the treated sheet with water.

Our presensitized planographic plate, as hereinabove described and illustrated provides a new article for cornmerce and industry. It is a plate which will yield high tive ma- Y i quality reproductions and long plate life, as well as fulfilling other objectives above set forth.

While we have described our novel article primarily in connection with its use asa lithographie plate, it has other uses. For example, our plates can be used to advantage in the photographic preparation of permanent metalname plates, instruction panels, templates, wiring dgarams, dial and scale faces, advertising specialties, signs, maps and the like. For these purposes, the plate is exposed to ultraviolet light through a photographic negative, followed by desensitizing and inking or developing as described above. The visible image may be produced by the use of an ordinary lithographic printing ink or an image developer, such, for example, as that disclosed above and also described in detail' in Hall Patent No. 2,754,279, granted Iuly l0, 1956, on application Serial No. 239,841, which was copending herewith. After the developed plate with its Visible image has been washed and dried, it may be used as such, or the surface may be further protected by spraying with a clear lacquer. Such plates may be fastened to machinery and the like, and made a permanent part thereof, to aid in the operation and maintenance of the machinery, and to identify its parts, its manufacture, etc.

Hereinabove we have attempted to describe and illustrate our invention in various details, and not to limit it. All'modifications and variations which are novel over the prior art and within the scope of the appended claims are contemplated.

What we claim is:

l. A presensitized, dimensionally stable plate suitable for lithographie printing and related uses, and capable of being shipped in light-proof packages, stored and then used Weeks or months after manufacture, comprising a thin sheet of metal having on at least one surface thereof a firmly bonded extremely thin water-insoluble protective vimage-retaining layer formed by treating said metal surfacer with a solution of awater-solu'ole. polyacid organic polymer-.capable of being formed into .a. self-sustaining lm and containing repeating acid units, said layer being the result of interaction between said metal sheet Vand said organic polymer and being substantially free of water-soluble excess` of saidpolymer, and coated'over and directly in contact with saidlayer a thincoating of a water-soluble light-sensitive diazo" resin sensitizer.

2. Avr presensitized, dimensionally stable-plate suitable for lithographie printing and related uses, and .capable of being shippedV in light-proof packages, stored and then used weeks or months after manufacture, comprising a thin sheet of metal having on at least one surface thereof a rmly bonded extremely thin water-insoluble protective image-retaining layer formed by treating said metal surface with a solution of a water-soluble organic polymer capable of beingformed into a self-sustaining film and containing repeating acid units selected from the group consisting of carboxylic and sulfonic acid units, said layer being the result of interaction between said metal sheet and said polyacid polymer and being substantially free of Water-soluble excess of said polymer, and coated over and directly in contact with said layer a thin coating of a water-soluble light-sensitive diazo resin sensitizer.

3. A presensitized, dimensionally stable plate suitable forv lithographie printing and relatedA uses, and capable of being shipped in light-proof packages, stored and then used weeks or months after manufacture, comprising a thin sheet of aluminum having on at least one surface thereof a firmly bonded extremely thin Water-insoluble protective image-retaining layer formed by treating said aluminum surface with a solution of a water-soluble linear acid addition polymer capable of being formed into a self-sustaining film and containing repeating carboxylic acid units, said layer being the result of interaction between said aluminum sheet and said linear acid addition polymer and being substantially free of water-soluble excess of said polymer, and coated over and directly in contact with said layer a thin coating of a water-soluble light-sensitive diazo resin sensitizer.

4. A presensitized, dimensionally stable plate suitable for lithographie printing and related uses, and capable of being shipped in light-proof packages, stored and then used Weeks or months after manufacture, comprising a thin sheet of metal having on at least one surface thereof a rmly bonded extremely thin water-insoluble protective image-retaining layer formed by treating said metal surface with a solution of a water-soluble linear acid addition polymer capable of being formed into a self-sustaining iilm and containing repeating carboxylic acid units, said layer being the result of interaction between said metal sheet and said linearacid addition polymer and being substantially free of water-soluble excess of said polymer and being permanently hydrophilic, and coated over and directly in contact with said layer a thin coating of light-sensitive diazo resin sensitizer, said diazo resin being characterized in that, upon exposure of the plate to ultraviolet light through a stencil or negative, it will react in the exposed portions, expelling nitrogen from theV molecule and forming a Water-insoluble hydrophobic and organophilic material, providing a printing image, the

thereof an extremely thin permanently hydrophilic water-1 insoluble protective image-retaining layer formed by treat: ing said surface with an aqueous solution of water-soluble polyacrylic acid, said layer being the result of interaction between said aluminum sheet and said polyacrylic acid and being substantially free of water-soluble excess of said polyacrylic acid, arid lover and in contact with said layer a thin coating of a light-sensitive diazo resin, said diazo resin,being characterized in that, upon exposure of the plate to ultraviolet light through a stencil or negative, it will react in the exposed portions, expelling nitrogen from the molecule and forming a water-insoluble, hydrophobic and organophilic material, providing a printing image, the light-sensitive materialbeing readily washed away from the unexposed areas, said image and said layer being tightly bonded together in the exposed areas, and said layer preventing the metal from causing decomposition of the diazo light-sensitive material, thus providing long shelf life for the presensitized plate.

6. A presensitized, dimensionally stable plate suitable for lithographie printing and related uses, and capable of` being shipped in light-proof packages, stored and then used weeks or months after manufacture, comprising a thin sheet of metal having on at least one surface thereof a iirmly bonded extremely thin water-insoluble protective image-retaining layer formed by treating said metal surface with a solution of a water-soluble polyacid cellulose polymer capable of being formed into a self-sustaining film and containing repeating acid units selectedfrom the group consisting of carboxylic and sulfonic acid units, said layer being the result of interaction between said metal sheet and said polyacid cellulose polymer and being substantially free of water-soluble excessof said polymer,

l2 and coated over and directly in contact with said layer a thin coating of a water-soluble light-sensitive diazo resin sensitizer.

7. .A plate suitable for use in lithographie printing and related uses, comprising a thin sheet of metal, cleaned to provide an essentially pure metal surface, having on said surface thereof an extremely thin permanently hydrophilic water-insoluble protective image-retaining layer formed by treating said surface with an aqueous solution of water-soluble polyacrylic acid, said layer being the result of interaction between said metal sheet and said polyacrylic acid and being substantially free of water-soluble excess of said polyacrylic acid, and over and in contact with said layer a thin coating of a water-soluble lightsensitive diazo resin sensitizer.

8. A plate suitable for us in lithographic printing and related uses comprising a thin sheet of aluminum, cleaned to provide an essentially pure aluminum surface, having on said surface thereof a rmly bonded extremely thin water-insoluble protective image-retaining layer formed by treating said metal surface with a solution of a Watersoluble polyacid organic polymer capable of being formed into a self-sustaining ilm and containing repeating acid units, said layer being the result of interaction between said metal sheet and said organic polymer and being substantially free of water-soluble excess of said polymer, and coated over and directly in contact with said layer a thin coating of light-sensitive diazo resin sensitizer, said,

References Cited in the file of this patent l Y UNITED STATES PATENTS 1,981,102 Hagedorn et al Nov. 20, 1934 2,063,631 Schmidt et al Dec. 8, 1936 2,100,063 Zahn Nov. 23, 1937 2,188,707 Crocker Ian. 30, 1940 2,561,814 Novotny et al Iuly 24, 1951 2,687,958 Neugebauer Aug. 31, 1954 2,694,639 Nadeau et al Nov. 16, 1954 2,699,392 Herrick lan. 11, 1955 2,714,066 Jewett et al. July 26, 1955 2,756,163 Herrick et al Iuly 24, 1956 2,760,431 Beatty Aug. 28, 1956 2,772,972 Herrick et al Dec. 4, 1956 2,937,085 Seven et al May 17, 1960 FOREIGN PATENTS 747,246 France Mar. 28, 1933 897,220 France May 15, 1944 904,255 France Feb. 15, 1945 OTHER REFERENCES La Technique des Reproductions Photomechaniques, L. P. Clerc, vol. I, 1947, Etablissements Bouzard-Calmels, Paris, pp. 356, 357 and 509-519.V

Chemical Abstracts, vol. 39, 1945, pages 589 and 590.

Organic Chemistry, Karrer, 4th Eng. Ed., Elsevier Pub. Co., N.Y., 1950, pp. 210-211.

Organic Chemistry, .Fieser and Fieser,V 2nd ed., D C. Heath & Co., Boston, 1950, p. 130. 

1. A PRESENSITIZED, DIMENSIONALLY STABLE PLATE SUITABLE FOR LITHOGRAHIC PRINTING AND RELATED USES, AND CAPABLE OF BEING SHIPPED IN LIGHT-PROOF PACKAGES, STORED AND THEN USED WEEKS OR MONTHS AFTER MANUFACTURE, COMPRISING A THIN SHEET OF METAL HAVING ON AT LEAST ONE SURFACE THEREOF A FIRMLY BONDED EXTREMELY THIN WATER-INSOLUBLE PROTECTIVE IMAGE-RETAINING LAYER FORMED BY TREATING SAID METAL SURFACE WITH A SOLUTION OF A WATER-SOLUBLE POLYACID ORGANIC POLYMER CAPABLE OF BEING FORMED INTO A SELF-SUSTAINING FILM AND CONTAINING REPEATING ACID UNITS, SAID LAYER BEING THE RESULT OF INTERACTION BETWEEN SAID METAL SHEET AND SAID ORGANIC POLYMER AND BEING SUBSTANTIALLY FREE OF WATER-SOLUBLE EXCESS OF SAID POLYMER, AND COATED OVER AND DIRECTLY IN CONTACT WITH SAID LAYER A THIN COATING OF A WATER-SOLUBLE LIGHT-SENSITIVE DIAZO RESIN SENSITIZER. 